The present invention relates to a pay television system and, more particularly, to an improvement of an apparatus for validating, in the pay television system, the accurate corresponding relation between a transmitting end and a receiving end.
Attention is directed to U.S. Pat. No. 4,024,574 issued May 17, 1977, which discloses a pay television system, and a validation method and apparatus for the pay television system.
The pay T.V. system, that is, the charged T.V. system of the type of wireless broadcasting has been thought out and developed in compliance with the demand for good and substantial programs even with charge, in view of annoying commercial messages which are unavoidable in programs offered free of charge to the viewers by commercial broadcasting and of decline in the quality of such programs owing to various restrictions. The system has advantages resulting from a wireless system that it can reduce expenses and time for laying a cable for broadcasting, and that number of subscribers to a pay T.V. system. This means that the feature of the pay T.V. system is worthy of attention.
In general, since the pay T.V. system is designed to serve only subscribers therefor, a normal composite T.V. signal is encoded to exclude non-subscribers therefrom. To be specific, a transmitting end includes an encoder for receiving the composite T.V. signal and encoding it according to a predetermined procedure, and such encoder has a key code under which the composite T.V. signal may be encoded. On encoding the signal, a data for decoding the encoded signal, which is formed on the basis of the similar key code, is added to a particular position of the composite T.V. signal. On the other hand, a decoder included in a receiving end receives the encoded composite T.V. signal, reads out the decoding data, and collates the received key code with the key code which has been preset in the decoder or performs a validation detecting operation, whereby it is possible to complete an accurate decoding process and then to output the normal composite T.V. signal, if the key code has been accurately preset in the decoder.
Accordingly, it is necessary in the pay T.V. system to validate the accurate corresponding relation between the key codes of the encoder and the decoder. For this validation, a validation signal which is formed of combination of the particular code signals is output from the transmitting end at the predetermined timing which differs from that of the decoding data, and the decoder then receives the validation signal and performs the validation detecting operation. Consequently, the decoder may generate a valid signal representing that the key code therein is effective on the decoded data signal. The generation of this valid signal means that the decoding operation is completely accomplished on the assumption that a billing data is recorded, when a program selector included in the receiving end is in an appropriate operation mode and a subscriber indicates his intention of watching a T.V. program.
FIG. 1 shows a block diagram of a conventional validation apparatus adapted for the transmitting end of the pay T.V. system. FIG. 2 shows a detailed circuit diagram of a portion of the validation apparatus shown in FIG. 1.
An encoded composite T.V. signal is applied to a code detector 1, a sync. signal detector 2 and a video processor 3, respectively. The code detector 1 detects a key code (validation signal) as a decoding data which has been added to the encoded composite T.V. signal in the transmitting end, and, in a key code circuit 4, the detected key code is validated with a key code which has been preset therein, and then the resulting validation is output therefrom as any one of "A", "B", "C" and "D" signals and is used to control a polarity flip-flop 5. Each of the "A", "B" and "D" signals causes the flip-flop 5 to output a signal representing one of two states thereof. The video processor 3 receives both a sync. signal output from the sync. signal detector 2 and a signal output from the flip-flop 5 (Q output), as control signals, decodes the encoded composite T.V. signal as described above, and then outputs a decoded composite T.V. signal. Also, the outputs from the flip-flop 5 are applied to a validation detector 6, and the detector generates a valid signal when the validation signal is received thereby and, alternatively, a non-valid signal when the validation signal is not received thereby. The valid signal enables an indicator such as a lamp 7, is applied to a billing data recorder 9, when the subscriber indicates his intention of watching a T.V. by turning a switch 8 ON, and, at the same time, sets a latch circuit 10. The set condition of the latch circuit turns a trigger switch 11 ON, and makes it possible to transmit the decoded composite T.V. signal to a television receiver (not shown). The billing data recorder functions, in the presence of the valid signal, to record a data representing a period during which the intention of watching is expressed, and to set a key code within the key code circuit 4.
Referring now to FIG. 2, the validation detector 6 comprises differentiators 20 and 21 which detect one state change from Q=1 to Q=1 (from the logic "1" of Q output to the logic "1" of Q output) and the other state change from Q=1 to Q=1, respectively, in the polarity flip-flop 5, an OR gate 22 for summing logically the output of each of differentiators 20 and 21, a state change counter 23 for counting the output of the OR gate 22, said counter in FIG. 2 being shown to include an AND gate 24 for generating the logic "1" when the count reaches "5", a validation field counter 25 for counting sequentially a state representing that the count of the counter 23 has reached a predetermined value, and a retrigger monostable multivibrator 26 triggered by the output of the validation field counter 25 for generating a valid signal.
It is assumed that, as disclosed in Nieson U.S. Pat. No. 4,024,574, the encoded composite T.V. signal from the transmitting end is so constructed that a signal or burst "f.sub.6 " is added to the normal composite T.V. signal to be positioned just before a vertical blanking signal therein and a sequence of code signals or bursts "f.sub.1 f.sub.5 f.sub.3 f.sub.1 f.sub.2 " each of which occupies the time period of a line is added thereto to be positioned after a equalizing pulse following a vertical sync. signal therein is completed, and the sequence of the code signals formed of "f.sub.1 f.sub.5 f.sub.3 f.sub.1 f.sub.2 " is arranged as a validation signal. On the other hand, the key code circuit 4 is so preset that the "D" signal is generated when the code detector 1 detects the code signal "f.sub.1 ", the "B" signal is generated when detects the "f.sub.2 " and the "f.sub.3 ", the "C" signal is generated when detects the "f.sub. 4 " and the "A" signal is generated when detects the "f.sub.5 ", respectively (f.sub.1 .fwdarw.D, f.sub.2 .fwdarw.B, f.sub.3 .fwdarw.B, f.sub.4 .fwdarw.C, f.sub.5 .fwdarw.D), whereby the "A" signal resets the polarity flip-flop 5 ("A" state), the "B" signal sets the flip-flop ("B" state) and the "D" signal toggles the flip-flop (changes from the "A" to the "B" or changes from the "B" to the "A"). Incidentally, the "C" signal is not effective on the operation of the illustrated circuit.
Referring now to FIG. 2, the operation of the circuit will be explained. At first, the code detector 1 detects the "f.sub.6 " signal, and the signal then acts to cause the validation field counter 25 to add "one" when the output of the AND gate 24 is the logic "1" and, on the contrary, to cause the counter 25 to be reset when the output is the logic "0". At the same time, the "f.sub.6 " signal also brings the polarity flip-flop 5 to an initial state "A" state). Then, the code detector 1 detects, in succession, a sequence of the code signals "f.sub.1 f.sub.5 f.sub.3 f.sub.1 f.sub.2 " as described above. As shown in the normal key code column of the following table [I], in successive sequence, the "f.sub.1 " signal causes the key code circuit 4 to output the "D" signal, thereby changing the polarity flip-flop 5 from the "A" state to the "B" state (Q=1.fwdarw.Q=1), the "f.sub.5 " signal causes to output the "A" signal, thereby resetting the flip-flop 5 to return it to the "A" state thereof (Q=1), the "f.sub.3 " signal causes to output the "B" signal, thereby setting the flip-flop 5 to assume the "B" state thereof (Q=1), the "f.sub.1 " signal causes to output the "D" signal, thereby changing the flip-flop 5 from the "B" state to the "A" state (Q=1.fwdarw.Q=1), and the "f.sub.2 " signal causes to output the "B" signal, thereby setting the flip-flop 5 to assume the "B" state thereof (Q=1).
TABLE [I] ______________________________________ NUMBER of STATE RESET f.sub.1 f.sub.5 f.sub.3 f.sub.1 f.sub.2 CHANGES ______________________________________ NORMAL A D A B D B .dwnarw. .dwnarw. B A B A B 5 NON- NORMAL 1 A D D B D B .dwnarw. .dwnarw. .dwnarw. B A B A B 5 2 A D D D D B .dwnarw. .dwnarw. .dwnarw. .dwnarw. .dwnarw. B A B A B 5 3 A D D D D D .dwnarw. .dwnarw. .dwnarw. .dwnarw. .dwnarw. B A B A B 5 4 A D A D D B .dwnarw. .dwnarw. .dwnarw. B A B A B 5 5 A D A D D D .dwnarw. .dwnarw. .dwnarw. .dwnarw. B A B A B 5 6 A D A B D D .dwnarw. .dwnarw. .dwnarw. B A B A B 5 7 A D D B D B .dwnarw. .dwnarw. .dwnarw. B A B A B 5 ______________________________________
The number of state changes, five times as shown in the table [I], in the polarity flip-flop 5, that is, "A.fwdarw.B.fwdarw.A.fwdarw.B.fwdarw.A.fwdarw.B", is counted by a state change counter 23, and then the AND gate 24 goes to an enabling condition. Consequently, under this condition, the output of the AND gate 24 is applied to the validation field counter 25 when the "f.sub.6 " signal is detected again by the code detector 1, and the counter 25 is advanced by one. If the forementioned operation is successively repeated by the predetermined number of times, the validation field counter 25 applies its output signal to the retrigger monostable multivibrator 26 and the multivibrator thus generates the valid signal.
As explained above in detail, in the pay T.V. system, the fundamental principle of the function of validation (the output of the valid signal) is that, on the basis of the validation signal transmitted from the encoder in the transmitting end, the decoder of the receiving end must be able to validate that the key code therein is preset to normally correspond to that in the encoder. In other words, when the valid signal is output in the decoder, there must be one to one correspondence between the key code preset in the decoder and the key code preset in the encoder. Further, in the conventional system shown in FIGS. 1 and 2, the validation signal is checked only by the number of state changes of the polarity flip-flop 5, as described above.
However, as exemplified in the following explanation, the conventional system may generate the valid signal even if the key code preset in the decoder is non-normal to the key code preset in the encoder. This means that, although the encoded composite signal is decoded non-normally, the billing data may be recorded when the intention of watching is expressed. Such unjustness is fatal to the pay T.V. system.
Each of the cases of "NON-NORMAL 1" to "NON-NORMAL 7" in the key code column of the table [I] illustrates a case where an non-normal valid signal is output. The case of "NON-NORMAL 1", for example, will be explained as follows.
Even if the key code of the key code circuit 4 is so preset non-normally that the preset key code is different from the normal key code (f.sub.1 .fwdarw.D, f.sub.2 .fwdarw.B, f.sub.3 .fwdarw.B, f.sub.5 .fwdarw.A) with relation to FIG. 2 and the signals of "f.sub.1 ", "f.sub.2 ", "f.sub.3 " and "f.sub.5 " cause the circuit 4 to output the signals "D", "B", "B" and "D", respectively (f.sub.1 .fwdarw.D, f.sub.2 .fwdarw.B, f.sub.3 .fwdarw.B, f.sub.5 .fwdarw.D), the state change in the polarity flip-flop 5 occurs five times. Therefore, when such operation is successively repeated by the predetermined number of times, the valid signal may be generated to record the billing data. However, when a further sequence of code signals "f.sub.5 f.sub.2 f.sub.1 f.sub.5 f.sub.1 " differing from the sequence of code signals "f.sub.1 f.sub.5 f.sub.3 f.sub.1 f.sub.2 " as described above is received after recording the billing data, each of the signals "D(=B)", "B", "D(=A)", "D(=B)" and "D(=A)" is output in response to the non-normal key code (f.sub.1 .fwdarw.D, f.sub.2 .fwdarw.B, f.sub.3 .fwdarw.B, f.sub.5 .fwdarw.D) and the encoded composite T.V. signal, therefore, is decoded non-normally, despite that each of the signals "A", " B", "D(=A)", "A", "D(=B)" as the control inputs to the polarity flip-flop 5 is expected to be output in response to the normal key code (f.sub.1 .fwdarw.D, f.sub.2 .fwdarw.B, f.sub.3 .fwdarw.B, f.sub.5 .fwdarw.A). Thus, it is unjust that the billing data may be recorded in spite of the non-normal decoding of the signal.
The disadvantages as mentioned hereinabove are caused by the fact that the "D" signal output from the key code circuit 4 acts as a toggle signal for the polarity flip-flop 5 and, more particularly, by the fact that, for example, the state change from the "B" state (set state) to the "A" state (reset state) in the polarity flip-flop 5 upon receipt of the "A" signal is equivalent to the state change from the "B" state to the "A" state upon receipt of the "D" signal.